1. Field of the Invention
The present invention relates to a picture display device that utilizes so-called electrooptical materials or electrooptical elements, such as liquid crystal, optical characteristics of which are subject to modulation by voltage, current, frequency or other electrical factors, and more particularly to a projection-type display device in which a display device provided with electrical elements such as transistors for controlling pixels for every pixel is used.
2. Description of the Related Art
As a projection system for projection-type display devices, there has been known a method called a rear projection system. In the rear projection system, an image is formed on the surface of a transmission type diffusion screen (hereinafter it is sometimes referred to as simply a screen) through a light source, enabling the image to be observed from the screen surface side opposite to the light source. A conventional device is shown in FIG. 5A. In FIG. 5A, reference numeral 500 denotes a main body; 501, a light source; 502, a liquid crystal panel and optical system; 503 and 504, mirrors; and 505, a screen.
Such display device of projection type (hereinafter it is sometimes referred to as a rear projection-type display device) irradiates a small-sized liquid crystal panel of 3 inch or less with an intense light from the light source to display an enlarged image on the screen by utilizing the optical system. For that reason, in order to make the display screen high in fineness and density, it is necessary further to narrow intervals between pixels of the liquid crystal panel or to reduce the size of the pixels and wirings themselves.
As indicated above, the development of highly fine liquid crystal panels is keenly attempted to obtain the display screen with high fineness and high density.
However, when the number of dot of the liquid crystal panel (the number of pixel) is increased to make the screen high in fineness, the line defect, point defect or the like tend to take place causing low yield. The term "point defect" means one pixel or an aggregate of more pixels which are malfunctioned by some reasons. Bright spots in which a white dot is displayed at the time of displaying black and unlit defects in which a black dot is displayed at the time of displaying white are main display malfunctions caused by the point defect.
That is especially the case with the projection-type display device in which the small-sized liquid crystal panel is irradiated with an intense light and an enlarged image is displayed on the screen using the optical system. Accordingly, upon use of the liquid crystal panel having at least one point defect, the bright spot 508 is displayed when displaying black, as shown in FIG. 5B, and the unlit defect 509 is also displayed when displaying white, as shown in FIG. 5C which make the display malfunctions prominent.
There is known a method in which the liquid crystal panel is processed with a laser beam to repair the panel, or the like. As means for repairing, such point defects, however, the liquid crystal panel of the projection type is difficult to be thus processed minutely because the pixel pitch or the like is very small. Accordingly, the repair thereof seems to become difficult when the fineness of the panel is further enhanced.